1. Field of the Invention
The invention relates to a fixing station assembly for fixing toner images produced on a recording medium in an electrostatic printing or copying machine and, more particularly, to apparatus for fixing powder toner images applied to a recording medium, such as a paper web, by means of solvent vapor.
2. Prior Art
Device arrangements for fixing powder toner images applied to a recording medium by means of solvent vapor for use in non-mechanical printing and copying machines utilizes electrostatic principles are known in the art, such as shown, for example, in U.S. Pat. Nos. 4,264,304 and 3,078,589. One such fixing station device of known construction is shown in FIG. 1. There, character images inked with toner powder material in a suitable developer station are carried on a paper web recording medium AT to a fixing station having a well-shaped receptacle BH through which the paper web is guided in a loop shaped manner. The paper web AT enters the upper end of the container BH about an upper support or guide member PF having an arcuately curved surface. The upper side of the guide member PF is disposed beneath the overhanging edge of the container wall LA1 at a narrow gap k. The paper web then passes downwardly into the container disposed in a lower area US which contains a supply of solvent vapor where it is threaded around a reversing drum UE adjacent the floor of the container. The web is then passed upwardly in the container and directed about a second reversing drum UR whereupon it leaves the container BH through the common opening of the container where the web initially entered. In order to limit escape of solvent vapor out of the container operating opening, the upper guide member PF and the second reversing drum UR are disposed to take up space within the the opening. The upper guide member is provided with a depending support or bridge member ST to which a seal DI1 is affixed, which seal is a lip type seal resting against the outer surface of the drum UR. Between the drum UR and the container LA2, a second seal DI2, which is also a lip seal, is provided. Also in order to limit escape of solvent vapor from the lower area fixation zone US, the container BH is typically provided with cooling coils KL disposed within the container walls or affixed to the walls over the fixation zone. Solvent vapor emerging from the fixation zone US will then arrive at a cooled zone causing the vapor to condense. Typically, the solvent vapor is heavier than air.
Solvent is delivered to the bottom of the container BH by means of an inlet tube RO. Disposed in the floor SS of the container is a heating unit HE, such as a heating coil for heating the solvent to a temperature such that it is vaporized. The guidance mechanism PF, UE, and UR for the paper web through the container BH is adjustable to facilitate threading of the paper web initially through the container. Accordingly, it is possible to raise the reversing drum UE from its lower fixing position within the fixation zone US to an upper position such that the drum may seat in a support bracket AN disposed in the operating opening. In order to move the reversing drum UE, an endless drive chain FK is connected about a guide roller RL1 stationarily mounted at the fixation zone, threaded about guide rollers RL2 and RL3 disposed adjacent the operating opening, and finally threaded around a suitably driven roller RL4. The roller RL2 is adjacent the support bracket AN in such a manner that the chain FK leaves from the fixation zone roller RL1 to the member AN. The reversing drum UE is suitably connected to the drive chain FK for movement therewith as disclosed in U.S. Pat. No. 4,264,304.
A problem arises in the operation of the conventional fixation station assembly in that toner powder disposed on the recording medium AT will deposit on the surface of the second reversing drum UR which, over the course of time, can lead to contamination, such as spotting, of the recording medium. It is known to position a stripper plate device DI2', in the form of a first lip plate which resiliently biases the recording medium against a stationary opposed lip plate, downstream of the drum UR for stripping toner accumulations from the recording medium. A drawback with this arrangement is that toner deposits accumulating in the flow gap between the stripper plates must be regularly cleaned or else there will be disruptions in the transport of the recording medium. Furthermore, if toner particles have not yet solidified on the recording medium, they will tend to deposit on the stripping plates of the device DI2' affecting printing quality.
An object of the present invention is to provide apparatus for a solvent vapor toner image fixing assembly used with electrostatic printing and copying machines which more completely reduces the level of solvent vapor losses without negatively influencing the feed operation or movement of the recording medium through the fixing station and which provides a more efficient and effective means for removing residues unavoidably collected on the recording medium during fixing operation.